*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
h1{
    text-align: center;
}
table{
    width: 100%;
    border-collapse:collapse;
}
table tr th,td{
   height: 40px;
   padding: 5px 10px;
   text-align: center;
   border: 2px solid green;
}